Field of the Invention
In servobrake systems for motor vehicles there is no mechanical, pneumatic or hydraulic connection between the activation unit, i.e. the brake pedal, and the wheel brakes, as is the case in conventional brake systems for motor vehicles. Although the driver can, by activating the brake pedal, influence the braking force by suitable control devices, his muscular force is not used, either in its entirety or in part, to generate the braking effect when the brake pedal is activated.
To date, servobrake systems have been used in vehicles on a series production basis only for utility vehicles, i.e. for trucks and buses. In such cases, compressed air or prestressed springs whose force is compensated in the released state by the force of a pneumatic cylinder on which compressed air acts are used as the operating energy. The braking effect is metered here by so-called service brake valves which are mechanically connected to the brake pedal and which, depending on the pedal position and pedal force, apply corresponding brake pressure to the wheel brake cylinders as taught in Bosch Technische Unterrichtung (Bosch Technical Education), Druckluftbremsanlagen, Gerxc3xa4te (Compressed Air Brake Systems, Equipment).
If the activation of the wheel brakes is controlled electronically as is known in the reference ATZ Automobiltechnische Zeitschrift (Motor Vehicle Technical Periodical) 98 (1996), pages 406 and 407; VDI Berichte (Reports) No. 1188, 1995, Potential Elektronisch Geregelter Bremssysteme (Potential of Electronically Controlled Brake Systems), the service brake valve is provided with sensors that measure the degree of deceleration desired by the driver. In the description of the concept for the electromechanical vehicle brake (also referred to as xe2x80x9cbrake by wirexe2x80x9d), an electronic brake pedal with a sensor system which is implemented with redundancy and with which the wishes of the driver are sensed is mentioned. The desired deceleration that is sensed in this way is then transmitted to the braking and control unit in the form of electronic signals.
It is accordingly an object of the invention to provide a brake value signal transmitter for an electrically controlled and activated brake system which overcomes the above-mentioned disadvantages of the prior art devices of this general type, which makes it possible to meter the braking effect in a sensitive fashion. Furthermore, the intention is that the braking effect will be largely proportional to the activation force of the brake pedal.
With the foregoing and other objects in view there is provided, in accordance with the invention, in combination with an electrically controlled and activated brake system, a brake value signal transmitter to be connected to a brake pedal of a motor vehicle and sensing movements of the brake pedal with at least one sensor and converting the movements into electrical signals, the brake value signal transmitter including: a cylinder having an interior wall defining an interior formed therein; a piston disposed in the interior of the cylinder; a rotatably mounted pressure rod connecting the brake pedal to the piston; and the interior of the cylinder defining a pressure space filled with a gas and at least partially with a hydraulic oil, the hydraulic oil bounding a gas-filled part of the pressure space with a variable volume, and the gas being compressed by the piston when the brake pedal is activated and causing a reaction force acting on the brake pedal to increase.
The advantages of the invention are, inter alia, that the pedal value signal transmitter does not require mechanical, hydraulic or pneumatic power assistance. Electrical energy is required merely to operate the sensors. In addition, the pedal characteristic curve can be freely selected. Thus, it is, for example, possible given a servobrake system of identical configuration to set a somewhat more severe pedal characteristic curve, i.e. with relatively high activation forces for the same pedal travel, for a sporty vehicle than for a limousine where the emphasis is on comfort.
In accordance with an added feature of the invention, there is a return spring disposed in the interior of the cylinder pressing the piston into a starting position.
In accordance with another feature of the invention, there is a felt ring, the piston having a groove formed therein receiving the felt ring, and the interior wall defining the interior is wetted with the hydraulic oil by capillary action of the felt ring that is in contact with the hydraulic oil.
In accordance with an additional feature of the invention, there is a pressure sensor, the rotatably mounted pressure rod has a pressure rod cylinder hole formed therein full of hydraulic oil and a pressure rod piston projecting into the pressure rod cylinder hole filled with the hydraulic oil, the pressure rod cylinder hole is connected to the pressure sensor for sensing a pedal force acting on the pressure rod.
In accordance with a further added feature of the invention, the area between the piston and the interior wall defines the pressure space, and including a pressure sensor subjected to and measuring a gas pressure generated by the piston in the pressure space.
In accordance with a further additional feature of the invention, there is a force sensor connected to the pressure rod and measuring a force acting on the pressure rod when the brake pedal is activated.
In accordance with another added feature of the invention, there is a pressure vessel having a pressure space formed therein and filled with a hydraulic oil and a gas provided above the hydraulic oil, the interior of the cylinder is completely filled with the hydraulic oil and is connected to and fluidically communicates with the pressure space of the pressure vessel.
In accordance with another additional feature of the invention, the cylinder has a lid component with an interior closing off the cylinder, the piston having a stem with a given diameter guided in the interior of the cylinder, and the piston having an area with a relatively smaller diameter than the given diameter of the stem and guided in the interior of the lid component.
In accordance with a concomitant feature of the invention, an annular space surrounds the piston and an equalization space is defined outside of the piston, the stem having at least one throttle hole formed therein connecting the annular space surrounding the piston to the equalization space.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a brake value signal transmitter for an electrically controlled and activated brake system, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.